[Patrick]

Now I'm baffled. Looking at the schematic, I get a strong audio signal on pin 3 of the 7C6. I also get a strong signal on the volume control, as well as the left side if R205. I get a very weak signal on the right side of R205.

I get no signal from the plate of the 7C6, and therefore to the input grid of the 7B5.

So how is this strong signal getting to the speaker? What path through what components could it be taking?